Page 173 - Concise Pathology for Exam Preparation ( PDFDrive )

158 SECTION I General Pathology

First exposure
Antigen- to antigen
presenting
cell
(APC) Antigen
(Tubercular
Antigen receptor MHC protein)
class II

IL–I2

Naive
CD4 T cell
Antigen
APC
(Macrophage/ Differentiation
dendritic cell)
TH1 cell

γ Interferon

Macrophage Activated
macrophage

Killing of mycobacteria • Formation of phagolysosome
(immunity) • ↑ No
• ↑Generation of free radicals

Monocyte recruitment • ↑ Tumour necrosis factor (TNF)

Differentiation of monocytes • ↑ Expression of MHC class II
into epithelioid cells molecules and increased antigen
presentation
• ↑ IL–1 and IL–I2
Granulomatous • ↑ PDGF ↑Collagen
response (hypersensitivity) synthesis
FLOWCHART 7.1. Sequence of events in primary tuberculosis.

• The lesion forming after primary infection is called ‘primary complex’ and it has
the following components:
a) Parenchymal component (Ghon focus): A subpleural, 1–1.5 cm parenchymal
lesion, often located just above or below the interlobar fissure (between the upper
and lower lobes).
b) Lymphatic component: Enlarged lymph nodes and lymphatics draining the paren-
chymal lesion.
• Fate of primary infection:
• Most primary lesions are asymptomatic and heal spontaneously by undergoing fibrosis
and calcification.
• In infants, children and immunodeficient individuals, primary tuberculosis may
progress to progressive primary tuberculosis (Flowchart 7.2).

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